1. Field of the Invention
The invention relates to a control arrangement for a working cylinder that may be actuated by a pressure medium having two separate adjustable regulating valves for both cylinder sides whereby each regulating valve is connected to a pressure medium source and a pressure medium outlet on one side and to the working cylinder on the other side.
2. The Prior Art
Traditionally, 4/3-port directional control valves (servo or proportional) are used for the control of double-action pressure medium motors or working cylinders and with which valves the user connections leading to both cylinder sides, the pressure medium connection and the tank or pressure medium outlet connection are all controlled together. The four controlling bevels necessary for the control are disposed rigidly on a common adjustment device, for example a piston-type control slide valve, whereby it is achieved, for example, in a simple manner that during application of pressure on one side of the cylinder, the respective other cylinder is correspondingly exhausted or connected to a tank.
Since this rigid coupling of the control of the two cylinder sides causes a number of difficulties, for instance during the control of differential cylinders as a result of different volumes at the two cylinder sides, whereas these difficulties may be avoided only with additional measures (for example by using so-called post suction valves.) A great deal to be desired are also the stiffness under load, precision in positioning and quiet operation at various loads and velocities as a result of pressure shocks, decompression impacts or the like. It has been already suggested, for example in xe2x80x9cxc3x96lhydraulik und Pneumatik (Oil Hydraulics and Pneumatics) 42 (1998) No. 4, page 240 and following pages, that the common 4/3-port directional control valves at both sides of the cylinder are to be replaced with two separate 3/3-port directional control valves for each cylinder side, which may be driven separately and independently from one another and which allows a great number of new possibilities for regulating cylinders. Stiffness under load for the drive may be increased according to need without problems, which results in an improvement for precision in positioning and quiet operation under various loads and velocities and which has as a result that the effects of the pressure shocks and decompression impacts are greatly reduced.
A similar control arrangement is further known from EP 654 608 B1, for example, in conjunction with a piston-less pneumatic cylinder, whereby the separate drive potential for each side of the cylinder is utilized to make possible a more efficient braking of the piston or thereby possible increase of the adjustment speed.
A disadvantage with the known embodiments of control arrangements of the noted type is of course the high demand for individual components and thereby also additional connection lines and the like, which requires also an increased effort in assembly and maintenance.
It is the object of the present invention to improve the control arrangement of the noted type in such a manner that the discussed disadvantages of the known embodiments are avoided and whereby especially the need of individual components to be assembled and to be connected is reduced and whereby a better layout of the control arrangement and simplified assembly and maintenance will be achieved.
This object is achieved according to the present invention with a control arrangement of the type mentioned above in that the adjustment elements of the two regulating valves are housed together in a common valve housing, which is further provided with pressure medium connections that are to be controlled for both sides of the cylinder and which in turn are provided with controlling bevels that communicate with the adjustment elements and which cylinder sides also have conduits which connect the control chambers. Thereby there is now, in an advantageous manner, a single compact unit employed again for the control of both sides of the cylinder, which is generally designed in the same manner, in regard to arrangement, the connections, assembly and maintenance, as the common 4/3-port directional control valve with rigid coupling for the control of the two cylinder sides mentioned above. The outwardly detectable and substantial differences of the novel embodiment are the separate adjustment possibilities of the two adjustment elements, which ensures the described functional division of the drive for the two sides of the cylinder. The required conduits and connections are arranged in or on the common valve housing, which naturally simplifies assembly and maintenance and which reduces possible faults or breakdowns. Given a corresponding arrangement of connections in the valve housing, the novel control arrangement can be used also very simply in the present application instead of the above-mentioned arrangement with a 4/3-port directional control valvexe2x80x94only provisions have to be made for the separate actuation of the two adjustment elements inside the common valve housing.
In a further embodiment of the invention it is proposed that the two adjustment elements are designed as adjustment pistons, which are disposed coaxial in the valve housing and which are adjustable by separate regulating drives being located opposite to one another at the outer frontal sides. This results in a structural simple configuration of the valve housing and in easy access to the two separate regulating drives and which also improves or simplifies assembly and maintenance.
In a further preferred embodiment of the invention, each adjustment piston may be guided within a control sleeve, which preferably holds both pistons and which can be arranged in the valve housing. This makes possible separate manufacturing of the sleeve from super hardened materialxe2x80x94which communicates with the controlling bevels of the adjustment pistonxe2x80x94or which also makes possible simple replacement of this sleeve after (excessive) wear.
In an additional preferred embodiment of the invention it is proposed that in order to counteract the negative effects of the uncontrollable pressure buildup caused by the pressure medium flowing into the outer frontal chambers after reaching the regulating drives through the guide clearance of the adjustment pistons, the outer frontal chambers on the regulating drives are connected with one another via axial bores in the adjustment pistons and via a servo-valve with the pressure medium outlet. In traditional directional control valves, the outer chamber on the regulating drives are often directly connected with the tank connections or via a throttle with a pressure connection and via a second throttle with the tank connection. The first configuration has the disadvantage of poor exhaust for the frontal chambers facing the regulating drives and development of pressure peaks, which could lead to instabilities in regulating; whereby in the second mentioned configuration a loss of power occurs additionally with its large throttle cross sections, whereas in case of small throttle cross sections the risk of activating the throttle exists and thereby an uncontrollable pressure buildup occurs in these chambers, which in turn may lead to the destruction of the regulating drive, which is normally not capable of bearing the maximum operational pressure. These disadvantages are avoided with the present embodiment of the invention and constant pressure is guaranteed in the frontal chambers on the regulating drives without additional loss of power.
Especially advantageous, within the above-mentioned context, is a yet further embodiment of the invention wherein the control sleeve between the two adjustment pistons are in an open position, preferably separated, and whereby the servo-valve is designed as an elastic sealing ring pre-stressed from the outside in radial direction over the opening, preferably over the ends of the two control sleeve segments. Naturally, besides the also known possibility, a traditional servo-valve designed as a spring-loaded ball valve may be provided in a conduit leading to the pressure medium outlet or the tank, for example. Furthermore, a structurally simple configuration can be realized with the described embodiment together with an open or separated control sleeve, whereby the achieved nearly constant pressure level leads to a high regulating stability in the chambers on the regulating drives without additional leakage (of pressure medium.)